Electronic commutator



M r 1947- D. s. MUZZEY, JR., r-rr AL 2,417,509

ELECTRONIC COMMUTATOR Original Filed Sept. 8, 1941 LOAD lnvezniors: Davidson/ilk M LJ. Jr.

Robzrf Duwagnc Miller [5Q w i wmemwm Patented Mar. 18, 1947 ELECTRONIC COMMU'lT ATOR David Saville Muzzey, Jr., Alexandria, Va., and

Robert Du Wayne Miller, Washington, D.C., assignors to Shell Development Company, San Francisco, Calii'., a corporation of Delaware Original application September 8, 1941, Serial N0. 410,010. Divided and this application July 28, 1943, Serial No. 496,688

This invention relates to a system of synchronous commutation, and has particular application in methods of geophysical exploration of underground formations, wherein an electric current commutated by electronic means is passed through the earth strata between grounded current electrodes, while the potential dilference generated in the earth by said current, or due to other causes, is measured between grounded potential electrodes by means of suitable indicating devices.

1 Claim. (Cl. 175-363) This application is a division of Patent 2,363,987, issued November 28, 1944. V

In exploring the ground by means of commutated direct current, it is customary to use so-called synchronous commutators, adapted to reverse in synchronism, and at a desired frequency, the connections between the source of ties, which are usually aggravated with time and wear, and which give rise to undesirable transient effects; insufliciently fast switching, giving an undesirably long current-oil time and resulting in an imperfect square-shape wave form, etc.

It is an object of the present invention to provide an electronic or thyratron commutator especially suitable for use in the electric exploration system of said patent.

It is also an object of this invention to provide an electronic commutator of flexible frequency characteristics, capable of delivering commutate currents of different predetermined constant fr quencies within a very wide range, such as from about one-half to about cycles or more.

It is also an object of this invention to provide an electronic commutator capable of extremely fast switching action, whereby current-off time periods may be reduced to extremely small values, such as 0.001 second.

These and other objects and features of this invention will be understood from the following 2 description taken with reference to the attached drawings, wherein:

The drawing shows a circuit diagram of the present are discharge or thyratron commutator unit. The single figure of the drawing shows the current-switching electronic commutator of the present invention connected to the D. C. source l8 by lines I! and I8, a source of approximately square wave-shape current by lines M and I5, and to theload 99 by lines,20 and 2|. Thiscommutator may comprise four large current carrying arc .discharge or thyratron tubes 81, 88, 89 and 90, which are biased so that each thyratron will fire only when a positive voltage pulse is applied ,to its grid. The primary windings of transformers 9|, 92, 93 and 94 are supplied with an approximately square wave current from lines l4 and IS. The secondary winding of each transformer is thus caused to develop a sharp voltage pulse when current flow is initiated in the primary over lines |4|5, and one of the opposite polarity when said current flow is discontinued. The grids of tubes 81 and 90 are connected to the secondary windings of the transformers so as to receive pulses of what shall be called positive polarity when the primaries are supplied with current, that is, at a time when a current i of an increasing intensity flows through said primaries, While the grids of tubes 88 and 89 are connected to receive pulses of negative polarity during this same time. On the other hand, when the supply of current to the primaries is dis- 5 continued, that is, at a time when a current of a decreasing intensity is flowing through said primaries, the grids of tubes 88 and 89 will receive pulses of positive polarity, while those of tubes 81 and 90 will receive pulses of negative polarity. Assume tubes 81 and 90 to be firing, their grids having received a positive voltage pulse from transformers 9| and 94. In such case, the next positive pulse will be on the grids of tubes 88 and 89 from transformers 92 and 93, and will cause these tubes to fire, which action will extinguish tubes 81 and 90 by means of condenser 95. The voltage applied to the load 99 will alternate.in direction, since when tubes 81 and 90 are firing, line 20 is positive with respect to line 2|, and when tubes 88 and 89 are firing, line 2| is positive with respect to line 20L In this way, direct current from generator or battery I6 is commutated to give a substantially square wave form current to the load 99 at a frequency depending on that of the current in lines I4 and II.

We claim as our invention:

In a system for passing a low frequency continuous reversing substantially square wave form current between two output terminals, as commutator circuit comprising two groups each having an equal even number of are discharge tubes, parallel inductive means for biasing the grids of one group of said tubes in a positive direction in response to a rise in the intensity of the current flowing through said inductive means, and for biasing the grids of the other group )1 said tubes in a positive direction in response to a fall in the intensity of the current fiowing through said inductive means, a plurality of connector means each between the cathode of a tube of the first group and the anode of a tube of the second group, all of said tubes being thus connected in pairs, condenser means connected between said connector means, output terminals connected in parallel with said condenser means between said connector means, a source of direct current, means connecting the positive terminal of said source to the anodes of one-half of the tubes in each of said groups, means for connecting the negative terminal 0! said source to the cathodes 4 of the other half of the tubes in each of said groups, means for supplying intermittent unidirectional voltage pulses to said parallel inductive means, whereby said two groups of tubes are alternately ignited by the biasing action of said inductive means and extinguished by the action of said condenser means and a low frequency continuous reversing substantially square iorm current is produced between said output terminals.

DAVID SAVILLE MUZZEY, Ja. ROBERT DU WAYNE MILLER.

REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 2,276,974 Howard Mar. 17 1942 2,294,395 Evjen Sept. 1, 1942 2,314,873 Evjen Mar. 30, 1943. 2,334,491 Jakosky Nov. 16, 1943 1,834,889 Bedford Dec. 1, 1931 1,723,888 Prince- Aug. 6, 1929 2,166,310 Lord July 18, 1939 

